In a conventional fastener driver, a pneumatically operated fastener driver is widely used in which a compressor is provided to generate a compressed air serving as a power source to drive the fastener driver. Since the pneumatically operated fastener driver requires the compressor, the compressor must be carried together with the fastener driver. This is troublesome when fastener driving operation must be performed while moving the faster driver from the first floor to the second floor. Thus, portability may be lowered. Further, a spot is required for installing the compressor. However, a working place is not always flat for installing the compressor. Thus, working place is also limited.
In order to overcome the problem in terms of limitation of working place and portability those attendant to the pneumatically operated fastener driver, an electrically powered fastener driver is provided in which a solenoid coil serving as a main drive source is driven by an electric power. In the fastener driver using the solenoid coil, low electric efficiency of the solenoid results such as about 5 to 20%. Therefore, a bulky driver is required in order to ensure large driving force. For example, an entire weight of the fastener driver incorporating the solenoid coil is three times as large as the weight of the pneumatically operated fastener driver to be used for driving the same kind of fasteners. Therefore, it would be very difficult to hand hold the solenoid-driven driver for a long period of time.
In order to improve electric efficiency of the electrically powered fastener driver using the solenoid, Japanese Patent Application Kokai No. H08-197455 discloses a fastener driver provided with a flywheel driven by an electric power. A rotational kinetic energy accumulated in the flywheel is utilized for driving the fastener driver.
In the electrically powered fastener driver using the flywheel, high electrical efficiency results such as 50 to 70%. Since driving energy for driving the fastener can be increased by increasing rotation number of the flywheel, entire weight of the flywheel type fastener driver can be reduced to about 1.5 times as large as the weight of the pneumatically operated fastener driver to be used for driving the same kind of fastener.
However, in order to perform fastener driving operation with a reduced reaction, kinetic energy accumulated in the flywheel must be transmitted to a fastener driving mechanism within an extremely shortened period such as several ten millimeter-seconds required for the fastener driving operation. In the fastener driver described in the JP reference, a complicated mechanism having the solenoid, a plurality of cams and balls is provided, so that a resultant fastener driver becomes bulky, which violates the advantage of compactness in the flywheel type fastener driver. Further, in accordance with the increase in the number of mechanical components, a possibility of a breakdown will be increased.